Science / project summary
This project is one of two components of a US-led international program, Overturning in the Sub-polar North Atlantic (OSNAP), designed to provide a continuous record of the full-water column, trans-basin fluxes of heat, mass and freshwater in the subpolar North Atlantic. The OSNAP observing system consists of two legs: one extending from southern Labrador to the southwestern tip of Greenland across the mouth of the Labrador Sea (OSNAP West), and the second from the southeastern tip of Greenland to Scotland (OSNAP East). The observing system also includes subsurface floats (OSNAP Floats) in order to trace the pathways of overflow waters in the basin and to assess the connectivity of currents crossing the OSNAP line. The location of the OSNAP East and West legs purposefully melds with a number of long-term observational efforts in the North Atlantic: the Canadian repeat hydrography program in the Labrador Sea; the German Labrador Sea western boundary array at 53°N; the global Ocean Observatories Initiative node in the southwestern Irminger Sea; the repeat hydrographic sections across the Irminger and Iceland basins; and the Ellett line in the Rockall region. Substantial international collaboration has been garnered for OSNAP, including measurement contributions from the UK, Germany, the Netherlands and Canada. Importantly, this observing system, in conjunction with the RAPID/MOCHA array at 26°N and the European Union NACLIM program measuring the Nordic Seas overflows, will provide the first comprehensive three-dimensional measure of the Atlantic Meridional Overturning Circulation (AMOC) and provide a means to evaluate inter-gyre connectivity in the North Atlantic. This collaborative project will implement the OSNAP West section and the OSNAP Float program. The primary observational components are: (i) a mooring array across the eastern margin of the Labrador Sea, where the subpolar boundary current enters the basin. This array will complement an analogous array across the western margin at the exit point of the Labrador Sea, maintained by institutions in Germany and Canada; (ii) a sequential release of acoustically tracked floats in the lower limb of the AMOC at the OSNAP East and OSNAP West boundary arrays. These floats will be seeded in the two densest components of North Atlantic Deep Water (NADW) over the four-year period of the measurement program (2014-2018). This research award includes support for a Science Accross Virtual Institutes (SAVI) that is co-funded by NSF's Office of International and Integrative Activities.